Miniaturised branch-line coupler with ultra-wide high suppression stopband

A compact branch-line coupler with an ultra-wide upper stopband is proposed based on a new type of transmission line. Consistent numerical and measurement results of the coupler are shown. The proposed branch-line coupler operating at 0.875 GHz exhibits a stopband from 2.8 to 12.9 GHz with suppression levels better than -20 dB. The occupied size of the proposed branch-line coupler is only 17.6% that of a conventional one operating at the same frequency.